#include <iostream>
//https://www.nowcoder.com/practice/03df7fa0950046a9ba564b4438f918a3?tpId=225&tqId=2181210&ru=/exam/oj&qru=/ta/primary-grammar-cpp/question-ranking&sourceUrl=%2Fexam%2Foj%3Fpage%3D1%26tab%3D%25E8%25AF%25AD%25E6%25B3%2595%25E7%25AF%2587%26topicId%3D225
using namespace std;

int main() {
    int num;
    int sum = 0;
    cin >> num;
    sum = (num / 2) * (num / 2 + 1); //公式计算
    cout << sum << endl;
    return 0;
}



